In recent years, operation speeds (operation clocks) of processors such as a central processing unit (CPU) have been increased due to an increase in a wiring density in internal structures of integrated circuits. However, a signal transmission speed in electronic transmission systems has reached almost its limit, which causes a bottleneck for increasing a processing speed of CPUs. Additionally, with an increase in an operation speed (operation clock) of CPUs, generation of a cross-talk noise due to high-density wiring and generation of electromagnetic interference (EMI) noise have become problematic. Therefore, it is necessary to take measures to eliminate such a noise problem.
As measures for eliminating the above-mentioned noise problem, an optical interconnection system (optical wiring system) using an optical waveguide has attracted attention. The optical interconnection method is capable of performing a transmission with a considerably larger band as compared to an electric transmission system. Thus, the optical interconnection method can contribute to a speed-up of a processing speed, and enables the construction of a signal transmission system using optical parts of a small-size and low-power consumption. Additionally, the optical interconnection method is capable of suppressing generation of a cross-talk noise and an EMI noise.
FIG. 1 is a cross-sectional view illustrating an optical transmission/reception device 200 having a conventional optical waveguide 100. The optical transmission/reception device 200 illustrated in FIG. 1 includes the optical waveguide 100, a light-emitting element 201 having a light-emitting part 201a, and a light-receiving element 202 having a light-receiving part 202a. The optical waveguide 100 includes a support board 101, a core layer 102, a clad layer 103, slots 104 and 105, and metal layers 106 and 107. An angle θ1 illustrated in FIG. 1 is 45 degrees.
In the optical waveguide 100, the core layer 102 and the clad layer 103 are formed on the support board 101. The clad layer 103 includes a first clad layer 103a and a second clad layer 103b between which the core layer 102 is situated. The slots 104 and 105 penetrate the core layer 102 and the clad layer 103.
The metal layer 106 is formed in a 45-degree inclination part of the slot 104, and the metal layer 107 is formed in a 45-degree inclination part of the slot 105. The light-emitting element 201 having the light-emitting part 201a is arranged above the slot 104 of the optical waveguide 100, and the light-receiving element 202 having the light-receiving part 202a is arranged above the slot 105.
In the optical transmission/reception device 200, a light emitted from the light-emitting part 201a of the light-emitting element 201 is incident on the optical waveguide 100, and the transmission direction of the light is changed by about 90 degrees. Then, the light travels in the slot 104 and is incident on the core layer 102. Because the refractive index of the core layer 102 is set higher than the refractive index of the clad layer 103, the light incident on the core layer 102 does not transmit to the clad layer 103 and propagates inside the core layer 102.
The light which propagates inside the core layer 102 reaches the metal layer 107, which changes the transmission direction of the light by about 90 degrees. Thus, the light deflected by the metal layer 107 is incident on the light-receiving part 202a of the light-receiving element 202. As mentioned above, the metal layers 106 and 107 formed in the 45-degree inclination parts of the slots 104 and 105 serve as an optical transmission direction changing part to change the transmission direction of the light traveling through the optical waveguide 100 in the optical transmission/reception device 200.
The optical waveguide 100 illustrated in FIG. 1 is manufactured by forming the core layer 102 and the clad layer 103 on the support board 101, forming the slots 104 and 105 having the 45-degree inclination parts, which penetrate the core layer 102 and the clad layer 103, in the core layer 102 and the clad layer 103, and further forming the metal layers 106 and 107 in the 45-degree inclination parts of the slots 104 and 105, respectively.
The slots 104 and 105 having the 45-degree inclination parts can be formed by a dicing method, a mold transfer method, or the like. As a method of forming the slots 104 and 105, there is suggested a method of dry-etching by patterning a photo resist using a photo mask having a mask pattern, which has an opening of which size or density gradually increases or decreases in a longitudinal direction of the optical waveguide 100. Also suggested is a method of controlling an amount of diffraction of a curing light by exposing a photo mask, when forming the core layer 102, while separating the photo mask from a surface of a material forming the core layer 102 by a distance equal to or larger than 500 μm.
As another example of the optical waveguide, it is suggested to use a mirror member having a mirror surface instead of forming the slots 104 and 105 having the inclination surfaces and the metal layers 106 and 107. Such an optical waveguide is fabricated by embedding the mirror members in a liquid material, which forms the optical waveguide, and, thereafter, curing the liquid material in the manufacturing process of the optical waveguide.
The following Patent Documents disclose conventional optical waveguides such as mentioned above.
Patent Document 1: Japanese Laid-Open Patent Application No. 6-265738
Patent Document 2: Japanese Laid-Open Patent Application No. 2001-272565
Patent Document 3: Japanese Laid-Open Patent Application No. 2002-131586
Patent Document 4: Japanese Laid-Open Patent Application No. 2007-183467
Patent Document 5: Japanese Laid-Open Patent Application No. 2007-183468
In the manufacturing method of the optical waveguide 100, there is a problem in that the process of forming the metal layers 106 and 107 on the 45-degree inclination parts by using a sputtering method, an electroless plating method or the like must be performed after formation of the slots 104 and 105 having the 45-degree inclination parts, which makes the manufacturing process of the optical waveguide 100 complicated.
This is because a mask to partially form the metal layers 106 and 107 in the process of forming the metal layers 106 and 107 on the 45-degree inclination parts, and the positioning between the mask and each of the 45-degree inclination parts of the minute slots 104 and 105 is difficult. Additionally, the metal layers 106 and 107 must be formed in the optical waveguide 100 one by one.
Moreover, in the structure using a mirror member having a mirror surface instead of the slots 104 and 105 having the inclination parts and the metal layers 106 and 107, a material which can be used for forming the optical waveguide is limited to a liquid material, which raises a problem in that a film-like material cannot be used as a material for forming the optical waveguide.